This invention relates to wire enamel. More particularly, this invention relates to a coating composition capable of forming an insulative coating on wire to provide a very low temperature solderability while maintaining satisfactory insulative properties.
Requirements for fast and reliable soldering require increased use of preassembled components which are subsequently dipped into a solder pot to decompose the insulation from the wire, for example, and cause it to be at the same time soldered to a terminal. The speed requirement in addition to the presence of other plastic materials in the preassembled package necessitates an insulated coating which will be capable of melting or disintegrating at as low a temperature as possible. Conversely, however, increased safety requirements mandate the need for an insulative material which will be capable of withstanding temporarily higher than normal operating temperatures such as, for example, when a short occurs causing a wire to heat up. This latter property can be defined as thermoplastic flow. Prescribed testing procedures by the National Electrical Manufacturers Association (NEMA) define the conditions under which the thermoplastic flow temperature of a wire is determined. (MW-1000-1973, procedure 50.)
Basically, the need for a low solderability temperature is, for most materials, the antithesis of the equally important need for good high-temperature insulation properties such as a high thermoplastic flow temperature. Quite surprisingly, however, we have found a particular coating composition which provides a surprisingly low solderability temperature yet provides a satisfactory thermoplastic flow temperature.